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                  实施第三剂新冠疫苗,要先考虑好这些问题

                  实施第三剂新冠疫苗,要先考虑好这些问题

                  Dana G. Smith 2021年09月13日
                  通过加强剂的注射来提高群体免疫力似乎是一个简单的解决方案,但现实要复杂得多。

                  注射加强剂疫苗与否,这是美国公共卫生专家正在面临的问题。今年8月,拜登政府宣布,所有美国民众将在9月底之前获得额外的新冠疫苗。但这一构想也只是初期阶段,在声明宣布之后,美国疾病控制中心(CDC)和美国食品与药品管理局(FDA)也与白宫分道扬镳,称其需要更多的数据才能够做出决定。但是,这两个机构仍然建议免疫功能低下者注射加强针。

                  这个问题的出现有着广泛的背景:越来越多的证据表明,疫苗的有效性会随着时间的推移而减弱。有研究表明,在完成疫苗接种之后,抗体水平逐渐下降,而这一降低与突破性感染风险增加呈现相关性。美国、英国和以色列的研究都显示,接种疫苗后的时间越长,突破病例就越多。对抗体隐蔽性很强的德尔塔病毒变体,也在今年夏天让已经接种完毕疫苗的人群中出现了不少突破性病例。

                  以色列是全球唯一一个为12岁以上的民众推出大规模注射加强剂计划的国家。最近两篇尚未经过同行评审的预印本论文显示,第三剂辉瑞(Pfizer)疫苗提高了抗体水平,也提高了对感染的保护能力。事实也可以支撑这些结论:以色列似乎已经在第三波疫情中转危为安,过去两周的新增病例比例已经下降。

                  随着德尔塔变种毒株继续在美国肆虐,通过加强剂的注射来提高群体免疫力似乎是一个简单的解决方案。但其实,现实要复杂得多。

                  一方面,尽管疫苗对感染的保护能力随着时间的推移而下降(据估计有效率最低只剩下50%),但对住院和死亡的保护仍然很强,仅从此前平均的95%略微下降到了85%。来自美国和以色列的医院数据证实了这一点:这两地的新冠肺炎住院病人大多数是尚未接种疫苗的人。

                  “有些人听到免疫力下降的新闻时,他们会想:‘天哪,5、6个月后我就不再有任何免疫保护了,说明疫苗根本不起作用。’但事实上数据并非如此。”宾夕法尼亚大学(University of Pennsylvania)的生物统计学教授杰弗里·莫里斯说:“免疫保护的减弱,并不意味着消失。它尤其意味着对感染的抵抗力的减少。而至于重症病例和住院病例,免疫保护并没有真的减少多少。”

                  因此,有一个问题一直存在争议:是每个人都应该注射第三剂,还是只应该注射那些风险最高的人群?有一种支持全面加强剂注射的观点:免疫是一个数字游戏——尽管从统计上看,发展成重症病例的可能性很小,但是,总体上感染的人数越多,住院和死亡的人数就会越多。通过在病例激增期间加强对感染的保护,就能够阻止病毒的传播,从而控制重症病例的人数。

                  以色列就是这么做的。尽管以色列的疫苗接种率很高,但是今年夏季仍然出现了病例激增,医院不堪重负。作为回应,以色列卫生部(Israeli Ministry of Health)强制几乎所有符合条件的民众注射了第三剂辉瑞疫苗。如果你没有注射加强剂,你的疫苗护照(vaccine passport)将会过期。

                  “以色列陷入了病例负担失控的危机之中,而这种情况现在才开始得到控制。所以他们竭尽了全力。”美国斯克里普斯转化研究所(Scripps Research Translational Institute)的所长埃里克·托波尔称,“我们知道,无论你多少岁,如果你接种了疫苗,而感染了突破病例,你仍然可以传染给其他人。这种可能性比未接种疫苗要小得多,但为了打破这一传染链,他们使出了浑身解数。现在问题是,我们也这样做的话,美国也会受益吗?这仍然是一个未知数。”

                  托波尔建议,与其向所有美国民众提供加强注射,还不如先提供给那些受益最大的人——免疫功能低下者——60岁以上的老年人以及一线医护人员。

                  “对60岁以上的人来说,提供加强剂的理由非常可靠……对卫生保健工作者也是,因为他们需要照顾病人。”他说,“而除此之外,我们还没有真正的数据……很有可能的是,随着年龄的下探,注射加强剂带来的好处会更少。”

                  以色列医生、新冠咨询团队前成员亚伊尔·刘易斯同意这个观点。他认为,第三剂疫苗不应该针对每个人,而应该只提供给最脆弱的人。其余人群能够通过非药物干预措施得到保护,例如佩戴口罩、频繁的核酸检测,以及接触病毒后的隔离。

                  “从以色列疫情激增的情况来看,对高危人群进行疫苗接种是非常重要的,这一点已经接近共识。”刘易斯说,“对这一点我举双手赞成。但接下来的问题是:‘剩下的所有人呢?’我可以代表我自己,我也能够告诉你,其实很多和我交谈过的同事都有类似的想法——一些非药物干预可能会更明智。”

                  此外,限制加强剂注射还有一个道德考量:疫苗剂量应该留给接种率低得多的国家。另一个考量则是疫苗资源仍然应该集中于未接种疫苗人群的接种。宾夕法尼亚大学的生物统计学家莫里斯担心,需要第三剂疫苗会让犹豫不决的人放弃接种疫苗,因为他们会认为(第三剂疫苗的接种)意味着疫苗没那么有效。

                  “在先前接种过疫苗的免疫保护基础上,增加一点点,这很好。但如果这需要以不能使更多未接种疫苗的人得到保护为代价,那这或许就会变成完全消极的一件事情。”他说,“未接种疫苗的人即使只接种一剂疫苗,也比之前接种过疫苗的人接种第三剂疫苗,要更能减少传播和重症病例的风险。”(财富中文网)

                  编译:杨二一

                  注射加强剂疫苗与否,这是美国公共卫生专家正在面临的问题。今年8月,拜登政府宣布,所有美国民众将在9月底之前获得额外的新冠疫苗。但这一构想也只是初期阶段,在声明宣布之后,美国疾病控制中心(CDC)和美国食品与药品管理局(FDA)也与白宫分道扬镳,称其需要更多的数据才能够做出决定。但是,这两个机构仍然建议免疫功能低下者注射加强针。

                  这个问题的出现有着广泛的背景:越来越多的证据表明,疫苗的有效性会随着时间的推移而减弱。有研究表明,在完成疫苗接种之后,抗体水平逐渐下降,而这一降低与突破性感染风险增加呈现相关性。美国、英国和以色列的研究都显示,接种疫苗后的时间越长,突破病例就越多。对抗体隐蔽性很强的德尔塔病毒变体,也在今年夏天让已经接种完毕疫苗的人群中出现了不少突破性病例。

                  以色列是全球唯一一个为12岁以上的民众推出大规模注射加强剂计划的国家。最近两篇尚未经过同行评审的预印本论文显示,第三剂辉瑞(Pfizer)疫苗提高了抗体水平,也提高了对感染的保护能力。事实也可以支撑这些结论:以色列似乎已经在第三波疫情中转危为安,过去两周的新增病例比例已经下降。

                  随着德尔塔变种毒株继续在美国肆虐,通过加强剂的注射来提高群体免疫力似乎是一个简单的解决方案。但其实,现实要复杂得多。

                  一方面,尽管疫苗对感染的保护能力随着时间的推移而下降(据估计有效率最低只剩下50%),但对住院和死亡的保护仍然很强,仅从此前平均的95%略微下降到了85%。来自美国和以色列的医院数据证实了这一点:这两地的新冠肺炎住院病人大多数是尚未接种疫苗的人。

                  “有些人听到免疫力下降的新闻时,他们会想:‘天哪,5、6个月后我就不再有任何免疫保护了,说明疫苗根本不起作用。’但事实上数据并非如此。”宾夕法尼亚大学(University of Pennsylvania)的生物统计学教授杰弗里·莫里斯说:“免疫保护的减弱,并不意味着消失。它尤其意味着对感染的抵抗力的减少。而至于重症病例和住院病例,免疫保护并没有真的减少多少。”

                  因此,有一个问题一直存在争议:是每个人都应该注射第三剂,还是只应该注射那些风险最高的人群?有一种支持全面加强剂注射的观点:免疫是一个数字游戏——尽管从统计上看,发展成重症病例的可能性很小,但是,总体上感染的人数越多,住院和死亡的人数就会越多。通过在病例激增期间加强对感染的保护,就能够阻止病毒的传播,从而控制重症病例的人数。

                  以色列就是这么做的。尽管以色列的疫苗接种率很高,但是今年夏季仍然出现了病例激增,医院不堪重负。作为回应,以色列卫生部(Israeli Ministry of Health)强制几乎所有符合条件的民众注射了第三剂辉瑞疫苗。如果你没有注射加强剂,你的疫苗护照(vaccine passport)将会过期。

                  “以色列陷入了病例负担失控的危机之中,而这种情况现在才开始得到控制。所以他们竭尽了全力。”美国斯克里普斯转化研究所(Scripps Research Translational Institute)的所长埃里克·托波尔称,“我们知道,无论你多少岁,如果你接种了疫苗,而感染了突破病例,你仍然可以传染给其他人。这种可能性比未接种疫苗要小得多,但为了打破这一传染链,他们使出了浑身解数。现在问题是,我们也这样做的话,美国也会受益吗?这仍然是一个未知数。”

                  托波尔建议,与其向所有美国民众提供加强注射,还不如先提供给那些受益最大的人——免疫功能低下者——60岁以上的老年人以及一线医护人员。

                  “对60岁以上的人来说,提供加强剂的理由非常可靠……对卫生保健工作者也是,因为他们需要照顾病人。”他说,“而除此之外,我们还没有真正的数据……很有可能的是,随着年龄的下探,注射加强剂带来的好处会更少。”

                  以色列医生、新冠咨询团队前成员亚伊尔·刘易斯同意这个观点。他认为,第三剂疫苗不应该针对每个人,而应该只提供给最脆弱的人。其余人群能够通过非药物干预措施得到保护,例如佩戴口罩、频繁的核酸检测,以及接触病毒后的隔离。

                  “从以色列疫情激增的情况来看,对高危人群进行疫苗接种是非常重要的,这一点已经接近共识。”刘易斯说,“对这一点我举双手赞成。但接下来的问题是:‘剩下的所有人呢?’我可以代表我自己,我也能够告诉你,其实很多和我交谈过的同事都有类似的想法——一些非药物干预可能会更明智。”

                  此外,限制加强剂注射还有一个道德考量:疫苗剂量应该留给接种率低得多的国家。另一个考量则是疫苗资源仍然应该集中于未接种疫苗人群的接种。宾夕法尼亚大学的生物统计学家莫里斯担心,需要第三剂疫苗会让犹豫不决的人放弃接种疫苗,因为他们会认为(第三剂疫苗的接种)意味着疫苗没那么有效。

                  “在先前接种过疫苗的免疫保护基础上,增加一点点,这很好。但如果这需要以不能使更多未接种疫苗的人得到保护为代价,那这或许就会变成完全消极的一件事情。”他说,“未接种疫苗的人即使只接种一剂疫苗,也比之前接种过疫苗的人接种第三剂疫苗,要更能减少传播和重症病例的风险。”(财富中文网)

                  编译:杨二一

                  To booster or not to booster, that is the question facing U.S. public health experts. In August, the Biden administration announced that all Americans would have access to an additional vaccine dose for COVID-19 by the end of September. But the declaration was premature, and the CDC and FDA have since split with the White House, saying they need more data before making the decision. (Both agencies still recommend that people who are immunocompromised get a booster shot.)

                  The question comes as evidence mounts that vaccine effectiveness does wane over time. Studies have shown that antibody levels gradually decline after vaccination, and lower antibody levels are associated with a higher risk of breakthrough infection. Research from the U.S., the U.K., and Israel all show an increase in breakthroughs the more time has passed since vaccination—although the Delta variant, which is more likely to evade antibodies, also played a role in the rise in cases among vaccinated people this summer.

                  In Israel, the only country to roll out a mass booster initiative for everyone over the age of 12, two recent preprint papers—which have not yet been peer reviewed—show that a third dose of the Pfizer vaccine raises antibody levels and improves protection against infection. Backing up the research, the country appears to have turned the corner on its third wave, and case rates have dropped for the past two weeks.

                  As Delta continues to wreak havoc in the U.S., boosting people’s immunity with a third shot seems like an easy solution. But the reality is more complicated.

                  For one thing, while vaccine protection against infection declines over time, by some estimates bottoming out around 50%, protection against hospitalization and death remains high, dipping only slightly from an average of 95% to 85%. Hospital data from the U.S. and Israel bear this out, where the vast majority of beds are taken up by people who are still unvaccinated.

                  “I think some people, when they hear waning immunity, they think, ‘Oh no, after five or six months, I no longer have any immune protection. The vaccine doesn't work at all.’ But the data doesn’t say that,” says Jeffrey Morris, a professor of biostatistics at the University of Pennsylvania. “The waning immune protection doesn’t mean it’s gone, it just means that it’s decreased, especially against infection. And when we look against severe disease and hospitalization, we don’t really see much waning there at all.”

                  As a result, one ongoing debate is whether everyone should get a third dose or only the groups that have the highest risk. An argument in favor of booster shots for all is that, in many ways, immunity is a numbers game. Even if the statistical likelihood of developing severe disease is small, the more people who are infected overall, the more hospitalizations and deaths there will be. By increasing protection against infection during a surge, you will stop the spread of the virus, and in turn limit the number of people with serious illness.

                  That was the rationale in Israel, where a surge in cases this summer overwhelmed hospitals despite a high vaccination rate. In response, the Israeli Ministry of Health all but mandated a third dose of the Pfizer vaccine for everyone who was eligible—if you didn’t get your booster shot, your vaccine passport expired.

                  “Israel has been kind of in a crisis with a runaway case burden, which is only now starting to get under control, so they pulled out all the stops,” says Eric Topol, director of the Scripps Research Translational Institute. “We know that if you’re at any age, if you’re vaccinated and you get a breakthrough, you still can transmit to others. The chances are much less than if you were unvaccinated, but to break the chain, they pulled out all the stops. The question is, would we benefit in the U.S. by doing that? And that’s an unknown.”

                  Instead of offering booster shots to all Americans, Topol suggests limiting eligibility to those who would benefit the most: people who are immunocompromised, over the age of 60, or frontline health care workers.

                  “I think the booster case is very solid now for people over age 60…and you can also make a pretty strong case for health care workers because they need to be taking care of the sick,” he says. “After that, we don’t really have data yet…but there’s going to be a lesser net benefit of the boosters, most likely, as we go down in age.”

                  Yair Lewis, an Israeli physician and former member of the country’s COVID-19 advisory team, agrees. Instead of boosting everybody’s antibody levels, he says a third dose should only be offered to the most vulnerable. The rest of the population should be protected through nonpharmaceutical interventions, such as masking, frequent testing, and quarantining after exposure to the virus.

                  “I think there was close to a consensus that from the way the surge was going on in Israel, it was really important to vaccinate the high-risk populations,” Lewis says. “I definitely supported that. Then there came the issue. ‘Okay, so are we going to boost the entire population?’ And I can speak for myself—I can also tell you that a lot of the colleagues I’ve spoken with think something similar—is that it probably would have been wiser to enforce some sort of light NPI, some nonpharmaceutical interventions.”

                  One reason for restricting booster shots is the ethical argument that the doses should be saved for countries where vaccination rates are much lower. Another is that resources should still be focused on improving uptake among those who remain unvaccinated. Morris, the UPenn biostatistician, worries that requiring a third dose will dissuade people who are on the fence from getting a vaccine because they’ll interpret it as meaning the vaccines aren’t very effective.

                  “To get some benefit from just supercharging a little bit of the immune protection that the previously vaccinated already has is nice, but if it comes at the cost of not being able to get more of the unvaccinated to be protected, it could be a net negative,” he says. “Getting even one dose in an unvaccinated person will reduce transmission and risk of serious disease way more than getting a third dose in a previously [vaccinated] person.”

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